One of the most popular devices involved in large scale integration (LSI) of electronic semiconductor circuits is the Metal-Insulator-Semiconductor (MIS) device or more specifically the Metal-Oxide-Semiconductor (MOS) device. Originally LSI technology was used to fabricate Field Effect Transistors (MOSFETS, IGFET, etc.) but more recently it is been applied to Charge-Coupled-Devices (CCDs), which incorporate integral photon detectors. The mechanism whereby storage of photon-produced minority charge carriers occurs in a surface depletion or inversion region of an MOS or MIS device is described by S. M. Sze in Physics of Semiconductor Devices published by J. Wiley 1969, pg. 486 and A. S. Grove in Physics and Technology of Semiconductor Devices also published by J. Wiley 1967. A description of charge coupled devices is given by G. F. Amelio, W. J. Betram, Jr. and M. F. Tompesett in the article "Charge Coupled Imaging Devices: Design Considerations" published in the IEEE Transactions on Electron Devices, Vol. ED-18, No. 11, Nov. 1971.
Theoretically charge coupled devices can be made from various semiconductor materials, so that the photoelectric effect can be extended to any spectral region for which a band-gap material exists. Actually; considering temperature dependence, structural stability, eash of fabrication and cost; the most practical base material is silicon, which limits the devices to rather high photon energies at the top of the visible spectrum. This is too restrictive for image intensifiers and thermal imaging devices which operate into the infrared region and far-infrared regions. Regardless of the material used, these devices have a further limitation in that their charge storage capability per unit area is orders of magnitude less than the maximum charge produced by a typical 3-5 micron detector now used in image intensifiers. The high level of charge is due to very high average levels of background signal. A few schemes have been advanced for lowering the average signal level including a.c. coupling and background subtraction (d. c. biasing), but these have involved complicated scanning and/or reductions in the useful signal.